Summary

Both luteal and nonluteal cells, i.e., macrophages, fibroblasts, vascular smooth muscle and endothelium, contain EGF receptors. Small luteal and nonluteal cells, however, contain more receptors than large luteal cells. The nuclei of both luteal and nonluteal cells also seem to contain EGF receptors. However, the pattern of nuclear receptor distribution differed with the receptor antibodies specific to the carbohydrate moiety and the binding sites on the extracellular domain of EGF receptor molecules. At the electron microscope level using the receptor antibody specific to the carbohydrate moiety, EGF receptors were found not only in plasma membranes, but also in rough endoplasmic reticulum, lysosomal vesicles, mitochondria and nuclei. The nuclear receptors are associated with nuclear membranes, condensed chromatin and the border between the condensed and dispersed chromatin. In conclusion, our results suggest that EGF may have steroidogenic and nonsteroidogenic roles in bovine corpora lutea and that transduction of EGF signals may also involve nuclear receptors.